FIVE WAYS TO SEE INSIDE THE BODY

Diagnostic tools include ionizing radiation, high-frequency sound and radio waves

Imaging tests are important tools that help doctors see inside the body to diagnose illness or injury.

But with an alphabet soup of names like X-ray, MRI, CT and PET, the tests can be confusing. Here is an overview of each test.

Your doctor will decide whether diagnostic imaging tests are needed and which ones are best, based on symptoms and the body part being examined. Start with your primary care physician, unless an emergency requires a trip to the ER.

• Plain film X-rays are the most common imaging tests and are most often used to view bones and organs. X-rays are high-frequency energy waves classified as ionizing radiation.

• Another test using ionizing radiation is the CT scan, or computed tomography scan. A CT scan creates a much more detailed image than an X-ray. Because it can scan large areas, this test often is used to view the abdomen, pelvis, brain or organs inside the chest.

During a CT scan, the patient lies on a table attached to a doughnut-shaped machine that takes X-ray images in narrow “slices” to create two- and three-dimensional pictures.

• A PET scan, or positron emission tomography, uses a radioactive tracer injected into the body that travels through the blood to collect in organs and tissues. The patient lies on a table inside a tunnel-shaped scanner that detects signals from the tracer and turns them into two- and three-dimensional images. A PET scan is particularly good at evaluating cancers and whether they are active or resolving.

• An ultrasound doesn’t use ionizing radiation but instead uses high-frequency sound waves and is often used to view organs like the gallbladder or kidneys. Many pregnant women have ultrasounds so the doctor can examine the fetus. During the procedure, a hand-held device called a transducer is moved over the body. The transducer emits sound waves and picks them up as they bounce back to create the image.

• An MRI, or magnetic resonance imaging, uses magnetic fields and radio waves to produce a picture. During the procedure, the patient must lie still on a table inside a machine containing the magnet. The test can take 30 minutes to an hour or more. The machine makes noises and some patients are given earplugs or a sedative if they feel uneasy.